The invention relates to a method for operating an internal combustion engine, in which an air filling in a combustion chamber is ascertained taking into account a pressure in an intake conduit. The invention also relates to a computer program, an electrical memory for a control and/or regulating device of an internal combustion engine, and to control and/or regulating device of an internal combustion engine.
A method of the type defined at the outset is known on the market. In many internal combustion engines, the pressure in an intake conduit is measured by means of a pressure sensor. Via a linear relationship, an air filling in the combustion chambers of the engine is calculated from the measured pressure. Above all in air-guided systems, knowledge of this air filling is important for correct metering of the fuel into the combustion chambers of the engine. Correct metering of the fuel in turn has effects on engine fuel consumption and emissions. Reference in this connection is made in general to German Patent Disclosure DE 197 56 919 A1.
Four-stroke internal combustion engines with camshaft overlap are also known. In such engines, in the region of top dead center between the expulsion stroke and the intake stroke, the outlet and inlet valves of a combustion chamber can be open simultaneously for a certain crankshaft range. As a result, an internal exhaust gas recirculation can be implemented, as a result of which among other effects a reduction in nitrogen oxide emissions can be achieved. However, it has been found that in such systems, if the camshaft overlap is great, the ascertainment of the air filling in the combustion chamber has so far been either complex or imprecise.
The present invention therefore has the object of refining a method of the type defined at the outset in such a way that even in systems with major camshaft overlap, the most precise possible determination of the air filling is possible on the basis of the pressure prevailing in the intake conduit.
In a method of the type defined at the outset, this object is attained in that the air filling is ascertained on the basis of a model, which as its input variables receives an rpm of a crankshaft and a ratio of the pressure in the intake conduit to an ambient pressure. In a computer program, an electrical memory, and a control and/or regulating device of an internal combustion engine, the stated object is attained accordingly.